Foreign Perspectives

Archive for the ‘Chemistry’ Category

Tuesday was a leap into unknown territory as we were all working on our own experiments. Having 44 separate experiments running rather than 22 made for a lot of slowing down as we all fought for the same pieces of glassware, chemicals and time from tutors and the York lab people. The net effect was that I didn’t get underway until rather later than anticipated.

To start with I was one of those using the “option A” method for the first stage of the experiment. That in itself was something of a challenge as it required rather larger than usual quantities of reagents with volumes measured in litres and made it feel like a small industrial process rather than a teaching lab scale. We originally thought that we’d be fighting over the two litre flasks at the end of the first stage but in practice our staggered starting times meant that it all went quite smoothly. This particular option is a little peculiar as once it gets going there’s a four hour reflux period followed by a flurry of activity and it’s done; the other option needs a good deal more constant attention. Overall, this option fits quite nicely into the day so, in principle, could be completed in one day.

That four hour break means that you can get going on preparing the phosphonium salt. This needs a little more thought as the salt you need usually isn’t the same one as you prepared earlier in the week so I needed the hex rather than pent variety; not everybody noticed that though. If you were really organised you could probably get that salt prepared on Tuesday but I think most people were working on it into Thursday morning. It would be worthwhile to try and get it done the first day as otherwise the final day can be quite hectic.

The evening tutorials covered how to write up a lab notebook which was quite different to my style for sure although I had good comments back on the first notebook this morning. Also covered or rather not covered was the EMA: we don’t get that ’til the last practical session is completed so don’t know what we’re aiming for yet.

Things kicked off much quicker this morning as we’d already checked all the glassware yesterday and we’d a better handle on where things were and what to do with them.

Starting with the carboethoxymethylenetriphenylposphorane that we’d made yesterday the plan was to prepare our alkene using ethanol as our reagent (the others starting from the same product used different reagents). There would have been more time between steps today but we were performing a direct synthesis and one using competing reagents so the second synthesis filled the gaps in the first which made for a very full day.

Reaching the end of this stage of the synthesis meant that it was time to analyse the end product using NMR spectroscopy, Infrared spectroscopy and gas chromatography. In practical terms, few people managed to complete the analyses as the various tests weren’t run until quite late in the afternoon so there wasn’t much time to do the analysis before we had to hand in our lab notebooks for assessment. Yup, on this course they actually do check your lab notebooks. This first assessment doesn’t count towards the final mark though and it’s intended to give us pointers as to how to do better when we’re writing up the second lab notebook which does count towards the final exam.

Tonights tutorial discussed our overall results as we’ll need to know how best to make a double bond that’s either E or Z. Also, we’d to pick which of the three substances we’d like to have a go at preparing (queen substance, farnesol and an insect pheromone). We’re going for the pheromone basically because loads of people started off choosing the  queen substance and farnesol is covered in some detail in the pre-course notes already.

Catering-wise, the lunch lets things down and the breakfast and dinner are excellent.

The day got off to a relatively slow start as it took quite a while to check that we’d all the various items of glassware on the checklist and that they were clean.

Our first experiment was to prepare carboethoxymethylenetriphenylposphorane from carboethoxymethyltriphenylphosphonium bromide. That requires a fair number of steps and helps a lot in getting back into the swing of practical chemistry with steps ranging from the simple dissolving of various chemicals, handling assorted chemicals that are toxic, irritants, flammable or indeed all of the above, separating out two different layers of chemicals, evaporating to get rid of solvents and finally weighing what you’ve made to see how efficient your methods were. Along the way, we picked up where the various solvents and reagents were in the lab, built increasingly fancy structures with the clamps, wrote it all down in a lab notebook and finished up with an overall yield of 87% which is pretty amazing. Since we weren’t fully up to speed that ended up taking most of the day and was quite a busy one.

All of us doing the stabilised Wittig procedure followed the above starting approach but we broke up into about half a dozen separate teams later in the afternoon as we used a variety of different reagents to make our alkene.

Catering-wise, the breakfast was excellent with a full English breakfast cooked quite nicely. Lunch was a bit of a let-down as it’s just sandwiches with tea/coffee. The evening lectures were optional with one on interpreting NMR spectra and the other on retro-synthetic analysis (which went way too quickly over the material for me so it’s just as well that the notes will be on the forum in due course).

With registration not starting ’til 2pm, I’d a very slow start to the morning and even managed to make a small start on the SXR376 ECA which I’m hoping to get working on a little bit during the week.

Breakfast is a properly professional affair here and Nottingham isn’t anywhere close to being in the same league for catering generally if today is anything to go by. The accommodation is equally a massive improvement with ensuite rooms and what seems like fairly new furniture too.

The first lecture wasn’t until 4.30pm and was split between the general introductory stuff, a broad overview of the week and a first look at the labs that we’ll be working in. Typically for chemistry, there seemed to be an awful lot of glassware and loads of bottles of reagents.

Dinner was a world away from Nottingham’s effort. We were even told that the chef would like us to be down at 6pm so that his food would be at its best! Maybe it’s more that he’d like to get away early but the impression is that he actually meant what he said, definitely a nice change.

The evening lecture at 7.30pm ran, very briefly, over the assessment before moving on to more detail about what we’ll actually be doing. We won’t get the ECA until August 2nd which I’m not too keen on as I like to have a look at what I’m aiming for so I’ll see if I can have a chat to some people who’ve done chemistry schools before to get at least a feel for it.

The second section of the lecture took a massive lurch into serious chemistry and it was only towards the end of it that I started to get my brain into “chemistry mode”. We’d to volunteer to take on board one of three reactions (stabilised Wittig, non-stabilised Wittig and HWE) with the 20-odd teams of two looking into a different reaction under each group.

Aside from not getting the ECA until well after we’ve left, the other differences from the biology schools that I’ve noticed so far are that the lab coats are supplied here whilst the lab notebooks aren’t so I’ve to acquire two of them tomorrow morning.

Thanks to the excellent pre-exam briefings by the course team, this was one exam that didn’t seem to cause people anything like the level of anxiety that others have been known to do.

As noted in the earlier post, the chemistry exam follows a very similar pattern from one year to the next. Almost to the point of being identical in many respects. Thus, question 1 is always a box diagram question and, as the course team commented, just about everyone gets full marks for it. In fact, the majority of the short questions are very similar from one year to the next and, because they follow the order of the books, you can pretty much bank on, say, question 7 being on whatever question 7 was on last year. That’s not to say that they’re all doable as it’s a massive course and few people revise everything but it does mean that selective revision is quite effective.

That follows through largely for the longer questions too although as the years have gone on, there seems to be more of a tendency to have one question covering parts of one or two other related areas ie if you’re doing selective revision then you’ll not be on totally firm ground all of the time. Moreover, the second and third longer sections are less easy use focused revision with than in the first section (which I think is always a choice between kinetics, orbitals and retrosynthetic analysis). Or perhaps it’s just that I’m less keen on the section C  and Dquestions?

What I did find pleasantly surprising was that even on my pessimistic in-exam estimate, I was well clear of 40%. That’s not so much because the exam was easy but that the whole exam is broken up into what’s effectively a very long list of short questions, albeit with several grouped into topics (ie the long questions).